Laminated metal sheet

ABSTRACT

A process for producing by simultaneous lamination a polymer/metal/polymer laminate, which process comprises laminating to one of the major surfaces of a metal sheet a composite polyester film (A) comprising an inner layer (A1) of a substantially non-crystalline linear polyester having a softening point below 150° C. and a melting point above 150° C. but below 240° C. and an outer layer (A2) of a linear polyester having a melting point above 220° C., and simultaneously laminating to the other major surface of the metal sheet a polyolefin-containing film (B) comprising a bonding resin which is an acid modified polyolefin-resin containing carboxyl or anhydride groups, the metal sheet having been heated to a temperature T 1  sufficient to cause softening of the polymer films and intimate contact with the metal sheet, the temperature T 1  being below the temperature at which the outer surface of the polyolefin-containing film is damaged during lamination, and re-heating the resultant laminate to a temperature T 2  sufficient to cause each of the polymer films (A1) and (B) to interact with and become bound to the respective surface of the metal sheet. The laminates are useful for forming into containers or various components thereof.

The present invention relates to a process for producing laminated metalsheet and to laminated metal sheet so produced.

Lamination of polymer materials to metal sheet such as metal strip is awell known and well documented technique. The resultant laminates havemany applications such as, for example, use for the manufacture of canbodies and can ends for containers for foodstuffs and beverages, and endcomponents and valve cups for aerosol containers.

For many applications, a polymer film is laminated to each of the twomajor surfaces of the metal sheet. In general, most of the knownlamination techniques are concerned either with the simultaneousapplication of polymer films of the same or similar composition toopposite faces of a metal sheet, or describe the lamination of polymerfilms having different compositions to the opposite faces of a metalsheet, each of the two different polymers being applied to the metalsheet in a separate step rather than simultaneously.

Whereas metal laminates having similar polymer coatings on both sides ofthe metal sheet or strip have many advantages, they are not suitable forall purposes. Thus, for example, while polyester coatings of the typedescribed in GB No. 2123746 have excellent formability, they are notreadily receptive to heat sealed closures, they are difficult to pigmentto an acceptable level of opacity at viable cost, and they change inappearance on retorting.

Polypropylene or polyethylene coatings such as those described, forexample, in GB No. 1324952 and EP No. 0062385 impart acceptablecorrosion resistance to the metal sheet but are relatively soft, damageeasily, have low melting points and relatively low gloss.

No single polymer embodies all of the various physical propertiesdesired in coatings for metal/polymer laminates which are intended foruse as can stock. Consequently it is found to be advantageous to use acombination of different polymers in a single polymer/metal/polymerlaminate and utilize appropriately the properties conferred to thelaminate by each polymer.

It is desirable, in many cases, to use dissimilar polymers laminated tothe two surfaces of the metal sheet thereby making use of the differentproperties of the different polymers.

It is preferable, from an economic point of view, to apply the differentpolymer coatings to the metal sheet in a simultaneous operation, therebyreducing operational costs. The simultaneous application of the twodifferent polymers can be achieved by the use of adhesives which areapplied separately to the two different polymeric films followed bylaminating these films simultaneously to the metal sheet. Alternatively,the required polymer films can be extrusion coated simultaneously in onesingle operation onto the two surfaces of the metal strip.

However, the first method is undesirable because it requires the use ofsolvent based materials which may contain biologically hazardouschemicals such as isocyanates and also involves lengthy cure schedules.The second method, which requires co-extrusion of molten polymers, woulddestroy the excellent properties of biaxially oriented polyestermaterials such as polyethylene terephthalate (PET), since such biaxiallyoriented materials cannot be extrusion coated and retain their excellentproperties.

Thermal lamination of biaxially oriented PET to metal strip is known,for example from GB No. 2123746. Similarly, thermal lamination ofpolypropylene films to metal strip is disclosed for example, in GB No.1324952 and U.S. Pat. No. 3679513, while thermal lamination ofpolyethylene films to metal strip is described, for example in EP No.0062385 and U.S. 4452375. However, the conditions described in thesedocuments for thermal lamination of polymer films having such variedproperties are not suitable for the simultaneous thermal lamination of apolyester film, especially biaxially oriented polyethylene terephthalatefilm, to one side of a metal strip, while at the same time thermallylaminating to the other side of the metal strip a polyolefin orpolyamide-containing film of a thickness which is economically ortechnically viable for can stock usage.

We have now found that simultaneous thermal lamination of a polyesterfilm to one side of a metal sheet and of a polyolefin orpolyamide-containing film to the other side of the metal sheet can bereadily achieved by matching the softening characteristics of thedifferent polymers on each side of the metal sheet by providing anintermediate layer of a substantially non-crystalline polyester layerhaving certain specific physical characteristics between the metal sheetand the polyester layer which it is desired to adhere to the metalsheet, and by laminating the polymer films to the metal sheet using athermal lamination process in which, in a first step, the polymer filmsare applied to the metal sheet at a first temperature which does notdamage the outer surface of the films as they pass through thelamination nip, and, in a subsequent step, the resultant laminate isre-heated by indirect means to a second higher temperature so as tocause the polymer films to react with, and adhere strongly to, the metalsheet.

According to a first aspect of the present invention there is provided aprocess for producing by simultaneous lamination a polymer/metal/polymerlaminate, which process comprises laminating to one of the majorsurfaces of a metal sheet a composite polyester film (A) comprising aninner layer (A1) of a substantially non-crystalline linear polyesterhaving a softening point below 150° C. and a melting point above 150° C.below 240° C. and an outer layer (A2) of a linear polyester having amelting point above 220° C., and simultaneously laminating to the othermajor surface of the metal sheet a polyolefin-containing film (B)comprising a bonding resin which is an acid modified polyolefin-resincontaining carboxyl or anhydride groups, the metal sheet having beenheated to a temperature T₁ sufficient to cause softening of the polymerfilm and intimate contact with the metal sheet, the temperature T₁ beingbelow the temperature at which the outer surface of thepolyolefin-containing film is damaged during lamination, and re-heatingthe resultant laminate to a temperature T₂ sufficient to cause each ofthe polymer films (A1) and (B) to interact with and become bound to therespective surface of the metal sheet.

According to a second aspect of the present invention there is providedpolymer/metal/polymer laminate comprising a metal sheet having a polymerfilm adhered to each of its major surfaces, the polymer films havingbeen adhered to the metal sheet by simultaneous thermal lamination, thepolymer film adhered to one major surface of the metal sheet being acomposite polyester film (A) comprising an inner layer (A1) of asubstantially non-crystalline linear polyester having a softening pointbelow 150° C. and a melting point above 150° C. but below 240° C. and anouter layer (A2) of a linear polyester having a melting point above 220°C., and the polymer film adhered to the other major surface of the metalsheet being a polyolefin-containing film (B) comprising a bonding resinwhich is an acid modified polyolefin resin containing carboxyl oranhydride groups.

The polyolefin-containing film (B) may be a mono-layered film of abonding resin which is an acid modified polyolefin resin containingcarboxyl or anhydride groups, or may be a composite film comprising anouter layer (B2) of a polyolefin or a polyamide adhered to an inner (ortie) layer (B1) of a bonding resin as defined above.

In a further embodiment of the present invention, the composite film (B)may include a further polyolefin or polyamide layer (B4) adhered to thesaid outer layer (B2) by means of an intermediate layer (B3) of abonding resin which is as defined above for layer (B1).

Preferably composite films (A) and (B) are films which have beenprepared by co-extrusion.

By means of the process of the present invention it is possible toobtain a metal/polymer laminate incorporating biaxially orientedpolyester materials such as polyethylene terephthalate on one side of ametal sheet with polyolefin or polyamide containing coatings on theother side of the metal sheet. By use of the present process bothpolymer coatings can be applied simultaneously while avoiding the use ofsolvent containing, environmentally undesirable, adhesives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, and 3 show lateral views of various polymer-metal-polymerlaminates according to the present invention.

FIGS. 4 thru 10 show shapes of typical products (metal containers andclosures) which can be advantageously produced from such composites.

FIGS. 11 and 12 show diagramatically the lamination process of thepresent invention.

The process of the present invention is carried out in a number ofstages. In a first stage, the metal is pre-heated to a temperature T₁ inthe range of 120° C. to 240° C., preferably 140 to 220° C., such thatthe outer surface of film (B) is not raised above its melting point inthe lamination nip, and preferably not above its softening point.

In a second stage, the films and metal are brought together in alamination nip thereby establishing intimate and uniform, wrinkle-free,contact. At this stage the contact layers are the inner layer (A1) ofamorphous polyester, metal and on the opposite side of the metal, theinner face of polyolefin or polyamide-containing film (B).

In a third stage, the resultant laminate is re-heated, preferably byinduction heating the metal core to a temperature T₂ above 230° C., butbelow the thermal or oxidative degradation point of the outer face ofthe polyolefin or polyamide containing film (B) or the temperature atwhich the outer layer physically degrades when quenched rapidly withwater. If desired, infra-red heating may be used.

While the outer surface of the polyester film (A) is maintained belowits melting point, but with the metal core above the melting point ofthe said polyester, rapid interaction occurs between the metal, theinner polyester layer (A1) and the polyolefin layer (B) In order toachieve this interaction, the laminate is held above 200° C. for 1 to 30seconds, preferably at about 250° C. for 2 seconds, and thereafter thelaminate is rapidly and uniformly quenched by water to a temperaturebelow the softening point of the resin having the lowest softeningtemperature.

We have found that provided the outer surface of the biaxially orientedpolyester film (A) remains below its melting point, a sufficientproportion of the excellent properties of the biaxially orientedpolyester film, e.g. polyethylene terephthalate, can be retained. Thetemperature in the post lamination zone can be varied to control theproperties, particularly formability, which are desired in the polyestercoating. Such control can be achieved quite readily if induction heatingis used to re-heat the laminate downstream of the lamination nip.Preferably a suitable pyrometer may be used to identify the temperatureof the polyester. Alternatively, devices that recognise the change frombiaxial orientation to crystalline non-oriented or amorphous polyestermay be used to indicate the critical state of the polyester film (forexample, an X-ray diffractometer).

The precise temperature T₁ to which the metal sheet should be heatedprior to lamination depends both on the thickness of the films to belaminated and also on the chemical nature of the said films. Thus,temperatures of approximately 120° C. and above, typically 140° C., aresuitable for a 20 micron cast polypropylene film, up to 230° C. for athicker 200 micron cast polypropylene film. Temperatures of 140° C. to270° are suitable for coextruded biaxially oriented polyethyleneterephthalate.

Polyamide containing films will tolerate slightly higher metaltemperatures than cast polypropylene and oriented polypropylene demandsa higher temperature than cast polypropylene, typically 200° C. for a 20micron film.

The temperature T₂ to be used on re-heating the laminate downstream ofthe lamination nip is typically in the range 230 to 270° C. The exacttemperature to be used will depend on the dwell time before the laminateis quenched. Temperatures higher than 270° C. lead to physical damage ofthe polyolefin film when it comes into contact with quench water andlead to melting of the polyethylene terephthalate films. The temperatureat the lower end of the said range is determined by the need to achievea satisfactory bond strength between the metal sheet and the polymerfilms attached thereto in the very short time during which the laminateis heated to the required temperature. Commercial operations generallydemand a dwell time of approximately two seconds only.

The metal substrate to which the polymer films are applied, typically inthe form of metal strip, is generally steel or aluminium or alloysthereof, typically a steel or aluminium based product used in thepackaging industry.

The gauge range is typically 0.05 mm to 0.4 mm for steel and 0.02 mm to0.4 mm for aluminium.

The steel may be coated with tin, preferably passivated by conventionalchromic treatments or alternatively may be in the form of nickel or zincplated steel, blackplate or phosphated blackplate, which is preferablychromate rinsed after phosphating.

The preferred steel finish is electrolytically chromium coated steel(ECCS) with a dual layer of chromium metal and chromium oxide. With suchsteels, the chromium metal and chromium oxide levels can vary widely.Typically, the chromium metal content ranges from 0.1 to 0.20 gm/m²,while the chromium oxide ranges from 0.005 to 0.05 gm/m², The ECCS iscommonly derived from deposition systems containing either sulphurcontaining or fluorine containing catalysts. The composite polyesterfilm (A) is preferably one which has been prepared by co-extrusion priorto application to the metal strip. The composite polyester film (A)comprises a thinner inner layer (A1) of a substantially non-crystalline(i.e. amorphous) linear polyester which has a softening point below 150°C. and a melting point about 150° C. but below 240° C., and a thickerouter layer (A2) having a melting point above 220° C., and preferablyhaving an intrinsic viscosity of from 0.5 to 1.1, preferably 0.6 to 0.8.

Preferably the outer layer (A2) is a biaxially oriented polyester suchas polyethylene terephthalate. Preferably the inner layer (A1) is alinear copolyester, for example an amorphous copolymer of approximately80 mole % ethylene terephthalate and approximately 20 moleethyleneisophthalate. Copolyesters of terephthalic acid and twoalcohols, for example ethylene glycol and cyclohexane-dimethanol, arealso suitable for use as the inner layer (A1).

Typically, the biaxially oriented polyester in outer layer (A2) has acrystallinity greater than 30%, preferably from 40 to 50%.

The crystallinity of a polyester material can be estimated by X-raydiffraction techniques as described in GB No. 1566422 or frommeasurement of density and applying the relationship:

    V.sub.c =(P-Pa) (Pc-Pa).sup.-1

where V_(c) =Volume fraction crystallinity

P=density of sample

P_(a) =density of amorphous material

P_(c) =density of crystalline material

P can be measured in a density column using zinc chloride/water orn-heptane/carbon tetrachloride mixtures.

The biaxially oriented film which may be used as the outer layer may beformed by stretching the amorphous extruded polymer in the forwarddirection at temperatures above the glass transition temperature of thepolymer by a factor of 2.2 to 3.8 and similarly in the transversedirection by 2.2 to 4.2. Where the laminated coating is to be used indeep drawing metal containers, the orientation is preferably limited tostretching by a factor approximately 2.5 in both forward and transversedirections.

Most preferred heat setting temperatures of biaxially oriented PET filmlie in the range 215° to 220° C.; lower heat setting temperatures may beused but are usually accompanied by an increased tendency for thepolyester film to shrink during lamination.

Typically the inner layer (A1) should be continuous and have a typicalthickness of about 2 to 5 microns. The ratio of the thickness of theouter polyester layer (A2) to the inner polyester layer (A1) is between12 and 4, with the total thickness of the combined layers being from 12to 25 microns.

If desired, the polyester layers may contain inorganic anti-blockingagents such as synthetic silica having an average particle size of from0.5 to 5 microns.

Also, if desired, the outer polyester layer (A2) may be pigmented usingconventional pigments such as titanium dioxide.

The principal function of the inner polyester layer (A1) is to heat sealto the metal surface at temperatures below the melting point of theouter polyester layer (A2). It is important that the inner layer shouldretain its amorphous nature after orientation and heat setting of thefilm. Furthermore the inner polyester layer (A1) should bond to themetal at temperatures which are compatible with the simultaneouslamination to the opposite side of the metal sheet of a polyamide orpolyolefin containing coating. This requirement is met by ensuring thatthe inner layer of polyester (A1) has a softening point compatible withthe temperatures needed to laminate a wide range of polyolefin orpolyamide based coatings. For this purpose the softening point should belower than 150° C., typically not greater than 130° C.

Preferably the polyolefin in outer layer (B2) is polypropylene, orpolyethylene, or an ethylene-propylene copolymer. If desired otherpolyolefins such as polymethyl pentene may be used.

The polyolefin-containing film (B) or the bonding resin layer (B1) in acomposite film (B) is an acid-modified polyolefin resin containingcarboxyl or anhydride groups. Typical acids for use in preparing suchacid-modified polymers are ethylenically unsaturated carboxylic acidssuch as acrylic acid, methacrylic acid, maleic acid, fumaric acid,crotonic acid, and itaconic acid. Typical anhydrides used for the samepurpose are ethylenically unsaturated carboxylic anhydrides such asmaleic anhydride.

The acid groups can be present as copolymers of ethylene, for exampleethylene/acrylic acid (EAA) or ethylene/methacrylic acid (EMMA).Typically the acid concentration is 5 to 15%.

The acid modification of the acid modified polymers can be obtained, fOrexample, by grafting maleic anhydride to a polyolefin such aspolypropylene, polyethylene, ethylene-propylene or ethylene-vinylacetatecopolymer. The graft can be introduced by techniques such as reactingmaleic anhydride with polyolefin in solution in an organic solvent andusing a free radical catalyst such as dibenzoyl peroxide or dicumylperoxide. Alternatively, an active centre can be introduced into thepolymer by using high energy radiation such as gamma rays or X-rays andthen reacting the resultant material with the anhydride.

The bonding resin preferably contains 0.05% to 0.5%, more preferably0.1% to 0.25% acid modification, measured by analysis of infra redadsorption at 1790 cm⁻¹, of resin pre-dried at 200° C. to convert acidfunctionality to anhydride functionality.

The anhydride graft-modified polyolefin can be diluted with furtherunmodified polyolefin to produce a bonding resin preferably having acontent of grafted acid (i.e. a graft level) of 0.02 to 0.6%, mostpreferably 0.2±0.05%. The diluting unmodified polyolefin can be the samepolyolefin which has been used to produce the acid modified polyolefin,or it can be a different polyolefin. Thus, for example, an acid modifiedlow-density polyethylene (LDPE) or linear low-density polyethylene(LLDPE) can be diluted with polypropylene, or an acid modifiedpolypropylene can be diluted with a polypropylene or an ethylenepropylene random copolymer.

The purpose of the inner layer (B1) of bonding resin is to tie the outerlayer (B2) of polyolefin or polyamide to the metal surface. Preferablywhen the outer polyolefin layer (B2) is a polyethylene, the bondingresin base of the inner tie layer (B1) is a polyethylene or ethylenecopolymer. Preferably when the outer polyolefin layer (B2) is apolypropylene homopolymer or an ethylene-propylene copolymer, thebonding resin base of inner tie layer (B1) is a polypropylene or anethylene propylene random copolymer. When the outer layer (B2) is apolyamide, the bonding resin layer can be based on a polyethylene or apolypropylene.

Preferably, for a bonding resin layer based on polypropylene, thebonding resin melt flow index is 3 to 30 gm/10 minutes, measured at 230°C. by the ASTM test No. D1238.

Particularly preferred bonding resin layers are based on randomethylene-propylene copolymers or blends of low-density polyethylene(LDPE) with polypropylene or blends of linear low-density polyethylene(LLDPE) with polypropylene.

A particularly preferred acid modified olefin copolymer ismaleic-anhydride modified ethylene vinyl acetate.

The layer of bonding resin (B1) in a composite polymer film (B) ispreferably of a thickness of from 1 to 10 microns.

In a further embodiment of the present invention, a further polyamide orpolyolefin layer (B4) may be adhered to the outer layer (B2) by means ofa further bonding resin layer (B3), the said bonding resin layer (B3)being as defined above for bonding resin layer (B1). If desired, any oflayers (B1) to (B4) may be pigmented in conventional manner, withtitanium dioxide for example. The preferred arrangement is for pigmentto be in layer (B2) or in layers (B2) and (B4). Preferably the outerpolyolefin or polyamide layer may contain inorganic anti-blocking agentssuch as synthetic silica having a particle size of from 0.5 to 5microns.

Throughout this specification, intrinsic viscosities are measured at 25°C. in O-chlorophenol solutions at a concentration of 5g/l.

The following Examples are now given by way of further illustration ofthe present invention.

EXAMPLES 1 to 24

Polymer/metal/polymer laminates were prepared by a lamination processperformed in apparatus as illustrated schematically in FIG. 11 or FIG.12 of the accompanying drawings. A metal sheet M was pre-heated to anappropriate temperature T₁ by a heater 1. Temperature T₁ is usuallywithin the range 120° to 220° C. A polyester film A was fed from a feedroll 2 and a polyolefin-containing film was fed from a feed roll 4 andlaminated to the opposite sides of the pre-heated metal sheet betweenlamination rolls 6, 8, typically having a diameter of 100-400 mm.Lamination was generally performed using a nip force of 200-400 N permetre between the lamination rolls.

In the lamination nip, intimate and uniform, wrinkle-free contactbetween the metal sheet and the polymer films is established. Downstreamof the lamination rolls the resultant laminate is re-heated, preferablyby use of an induction heater 10, to a temperature T₂ at which each ofthe polymer films A and B will interact with and become bound to themetal sheet. Temperature T₂ is usually within the range 230 to 270° C.The metal polymer laminate is held at temperature T₂ or a temperatureslightly below T₂ for a short period of time, usually no more than 2seconds, and is then rapidly and uniformly quenched with water to atemperature below the melting point of the polyolefin-containing film(B). Quenching can be performed in any conventional manner, buttypically can be performed by passing the laminate through a tank 12 ofwater as shown in FIG. 11 or by passing the laminate through curtain 14of quenching water as shown in FIG. 12.

In general, the process illustrated in FIG. 11 with the lamination beingperformed in a vertical mode is preferred. Vertical movement of themetal strip through the lamination stage tends to allow a higher quenchrate and gives better and more uniform quenching.

FIG. 11 also shows a schematic diagram of a typical temperature profilewhich would be found in the process illustrated in the apparatus of FIG.11.

Table 1 sets out the types of polymer which were laminated to the metalstrip and the thickness of each layer. The conditions used to performthe lamination and the results obtained are given in Table 2.

The polyester film A applied to the metal strip may be in the form of afilm having a single layer (as in the case of Examples 11 to 14 whichare given by way of comparison); in these cases the nature of thepolymer is set out in the column in Table 1 headed A1. Alternatively thepolyester film A may be a composite film of an inner layer A1 and anouter layer A2, usually prepared by co-extrusion of the appropriatepolymer films; such films are films in accordance with the invention.

The polyolefin film B may contain only a single layer B1 as in the caseof the laminate illustrated in FIG. 1, or may be a composite filmcontaining a plurality of layers B1, B2, B3, B4, prepared typically byco-extrusion of the appropriate polymer films.

FIG. 1 of the accompanying drawings illustrates a polymer/metal/polymerlaminate having a composite polyester film A1/A2 laminated on one sideof a metal sheet M with a single layer polyolefin-containing film B1laminated to the opposite side of the film. The laminates which are thesubject of Examples 1 to 3, 17 and 18 are laminates having thisstructure.

FIG. 2 of the accompanying drawings illustrates a polymer/metal/polymerlaminate having laminated thereto a composite polyester film A1/A2 onone side of the metal sheet and a composite polyolefin-containing filmB1/B2 laminated to the opposite side of the metal sheet. The laminateswhich are the subject of Examples 4 to 8, 15, 16 and 19 to 24 arelaminates having this structure. Examples 9 and 10 have this structurebut carry two additional outer layers, B3 and B4 on the polyolefincoated side of the metal sheet.

FIG. 3 illustrates a polymer/metal/polymer laminate in which each ofpolymer films A and B have a single layer. The films of Examples 11 and12 are of this type.

The metal/polymer laminate structures of Examples 1 to 10 and 15 to 23are structures suitable for processing in accordance with the presentinvention. Table 2 gives examples of the lamination behaviour underdifferent conditions of the various laminate structures set out in Table1.

Table 2 shows that if the temperature of the metal sheet on laminationis raised to a level which is too high, the polyolefin coatings adhereto the lamination rolls (Cases D, E, F and I). Furthermore, if thetemperature of the metal sheet on lamination is kept too low, and nopolyester inner layer (A1) in accordance with the invention is present,the polyester film does not adhere adequately to the metal sheet (CasesG and H).

                                      TABLE 1                                     __________________________________________________________________________    COMPOSITION OF METAL POLYMER LAMINATES                                        EXAMPLE                                                                              LAYER A2                                                                             LAYER A1                                                                              M  LAYER B1 LAYER B2                                                                              LAYER B3 LAYER                      __________________________________________________________________________                                                       B4                          1     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 1                                             (12μ)                                                                             (3μ)    (20μ)                                              2     As above                                                                             As above                                                                              E  Bonding Resin 2                                                               (25μ)                                              3     As above                                                                             As above                                                                              E  Bonding Resin 3                                                               (50μ)                                              4     As above                                                                             As above                                                                              E,A                                                                              Bonding Resin 1                                                                        Polypropylene                                                        (2μ)  (18μ)                                     5     As above                                                                             As above                                                                              E  Bonding Resin 2                                                                        High density                                                         (5μ)  Polyethylene                                                                  (20μ)                                     6     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 2                                                                        Low density                                        (12μ)                                                                             (3μ)    (5μ)  Polyethylene                                                                  (20μ)                                     7     As above                                                                             As above                                                                              E  Bonding Resin 3                                                                        High density                                                         (5μ)  Polyethylene                                                                  (20μ)                                     8     As above                                                                             As above                                                                              E,A                                                                              Bonding Resin 3                                                                        Low density                                                          (5μ)  Polyethylene                                                                  (20μ)                                     9     As above                                                                             As above                                                                              E,A                                                                              Bonding Resin 1                                                                        Polypropylene                                                                         Bonding Resin                                                                          Polyamide                                           (2μ)  (29μ)                                                                              (2μ)  (5μ)                    10     As above                                                                             As above                                                                              E  As above As above                                                                              As above Polymethyl-                                                                   pentene                                                                       (5μ)                    11            Biaxial PET                                                                           E  Bonding Resin 1                                                    heat set above                                                                           (20μ)                                                           215° C.                                                                (12μ)                                                        12            Biaxial PET                                                                           E  Bonding Resin 1                                                    heat set below                                                                           (20μ)                                                           210° C.                                                                (12μ)                                                        13            Biaxial PET                                                                           E  Bonding Resin 1                                                                        Polypropylene                                             heat set above                                                                           (2μ)  (18μ)                                                  215° C.                                                                (12μ)                                                        14            Biaxial PET                                                                           E  Bonding Resin 1                                                                        Polypropylene                                                                         Bonding Resin                                                                          Polyamide                                heat set above                                                                           (2μ)  (29μ)                                                                              (2μ)  (5μ)                                  215° C.                                                                (12μ)                                                        15     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 1                                                                        Polypropylene                                      (12μ)                                                                             (3μ)    (10μ) (90μ)                                    16     PET    Polyester A                                                                           E  Bonding Resin 1                                                                        Polypropylene                                      (13μ)                                                                             (5μ)    (2μ)  (18μ)                                    17     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 4                                             (12μ)                                                                             (3μ)    (50μ)                                             18     As above                                                                             As above                                                                              E  Bonding Resin 5                                                               (50μ)                                             19     As above                                                                             As above                                                                              E  Bonding Resin 1                                                                        Polypropylene                                                        (2μ)  (18μ)                                    20     As above                                                                             As above                                                                              E  Bonding Resin 6                                                                        As above                                                             (2μ)                                              21     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 7                                                                        Polypropylene                                      (12μ)                                                                             (3μ)    (2μ)  (18μ)                                    22     As above                                                                             As above                                                                              E,A,                                                                             Bonding Resin 1                                                                        Polypropylene                                                     T,B                                                                              (2μ)  (38μ)                                    23     Biaxial PET                                                                          Polyester A                                                                           E  Bonding Resin 1                                                                        Polypropylene                                      having low                                                                           (3μ)    (2μ)  (18μ)                                           draw ratio                                                                    (2.5 by 2.5)                                                                  (12μ)                                                               24            Biaxial PET                                                                           E  Bonding Resin 1                                                                        Polypropylene                                             (12μ)   (10μ) (90μ)                                    __________________________________________________________________________     KEY TO TABLE 1                                                                Polyester A: In Examples 1 to 10, 15, 17-22 and 23 a noncrystalline (i.e.     amorphous) polyester which was an 80:20 copolymer of ethylene                 terephthalate and ethylene isophthalate was used. The softening point of      the polyester was below 150° C. and the melting point of the           polyester was 210° C. The intrinsic viscosity of the polyester was     from 0.6 to 0.7.                                                              In Example 16, the amorphous polyester was a copolyester of terephthallic     acid and ethylene glycol and cyclohexane dimethanol. The softening point      of the polyester was below 150° C. and the melting point of the        polyester was 180° C. The intrinsic viscosity of the polyester was     above 0.9 and below 1.1.                                                      Bonding Resin 1: Maleic anhydride graft modified ethylene propylene rando     copolymer having graft levels of about 0.2 0.05.                              Bonding Resin 2: Maleic anhydride graft modified polyethylene having graf     levels of about 0.08 ± 0.05.                                               Bonding Resin 3: Ethylene/Acrylic Acid Copolymer (EAA) typically having 6     or 9% acrylic acid.                                                           Bonding Resin 4: Ethylene Methacrylic Acid Copolymer (EMAA) typically         having 9% or 12% methacrylic acid.                                            Bonding Resin 5: Maleic anhydride graft modified ethylene vinylacetate        copolymer having graft levels of about 0.08 ± 0.05.                        Bonding Resin 6: Maleic anhydride graft modified polypropylene homopolyme     having graft levels of about 0.2 ± 0.05.                                   Bonding Resin 7: Maleic anhydride graft modified ethylenepropylene block      copolymer having graft levels of about 0.2 ± 0.05.                         PET: Polyethylene terephthalate.                                              Biaxial PET: Biaxially oriented polyethylene terephthalate having a           melting point of 255° C.                                               Polyamide: Nylon 6.                                                           Metal Strip M: This may be ECCS (represented by E), aluminium or an alloy     thereof (represented by A), tinplate (represented by T), or blackplate        (represented by B).                                                      

                                      TABLE 2                                     __________________________________________________________________________                 METAL TEMPERATURE (°C.)                                                Before  After                                                    CASE                                                                              EXAMPLE NO.                                                                            Lamination                                                                            Lamination                                                                            LAMINATION BEHAVIOUR                             __________________________________________________________________________    A   1 to 10, 16-23                                                                         140-150 250     Satisfactory                                     B   9, 10    160-180 250     Satisfactory                                     C   15       170-190 250     Satisfactory                                     D   1 to 8, 16-22                                                                          >170    250     Polyolefin adheres                                                            to lamination roll                               E   9, 10    >200    250     Polyolefin/Polyamide                                                          adheres to                                                                    lamination roll                                  F   15       >210    250     Polyolefin adheres                                                            to lamination roll                               G   11-13     150    250     PET does not adhere                                                           in lamination stage                              H   14, 24    180    250     PET does not adhere                                                           in lamination stage                              I   11-14, 24                                                                               270    250     Polyolefin coatings                                                           adhere to the                                                                 lamination roll                                  __________________________________________________________________________     COMMENTS                                                                      Cases A, B and C  Illustrate the materials and process described in this      invention, successfully applied.                                              Cases D, E and F  Illustrate the limits imposed by the polyolefin coating     on the lamination temperature. The polyester laminated successfully in        D-F.                                                                          Cases G, H and I  Combinations of materials described in the prior art,       showing their incompatibility at the low (G,H) and high (I) lamination        temperatures needed to laminate polyolefins and biaxially oriented PET        monofilms respectively.                                                  

EXAMPLES 25 to 51 (see Table 3)

These Examples illustrate a number of components for metal packagingcontainers and closures which can be advantageously produced from thepolymer/metal/polymer laminates produced in accordance with the presentinvention. Illustrations of the typical shapes of typical products areshown in FIGS. 4 to 10 of the accompanying drawings.

Table 3 indicates the nature of the metal sheet (M), the types ofpolymer films (A) and (B) which are laminated thereto, and states foreach application which polymer film constitutes the external coating (C)of the product and which polymer film constitutes the internal coating(D) of the product.

The laminates described in Examples 25 to 31 were formed by conventionaltechniques into food can ends such as that illustrated in FIG. 4 of theaccompanying drawings.

The laminates described in Examples 32 to 34, and 51 were formed byconventional techniques into drawn cans (draw-redraw cans) such as thatillustrated in FIG. 5 of the accompanying drawings.

The laminates described in Examples 35 to 38 were formed by conventionaltechniques into easy open beverage can ends such as that illustrated inFIG. 6 of the accompanying drawings.

The laminates described in Examples 39 and 40 were formed inconventional manner into drawn wall ironed cans such as that illustratedin FIG. 7 of the accompanying drawings.

The laminates described in Examples 41 to 43, 44 and 45, and 46 to 50were formed in conventional manner into aerosol cups, aerosol cones, andaerosol domes such as those illustrated respectively in FIGS. 8, 9 and10 of the accompanying drawings.

The ECCS used in Examples 25-29, 31-36 and 41-51 was a conventionalcommercial product supplied by the British Steel Corporation and wasgiven its ECC treatment in a chromic acid medium containing sulphuricacid catalyst (Type 1). The ECC treatment applied to the steel inExample 30 was in a chromic acid medium containing HBF₄ catalyst (Type2).

The aluminium used in Examples 37-40 was treated in a chromicacid-phosphoric acid medium in the aluminium strip mill after coldrolling and cleaning.

The tinplates used in Example 22 had tin coating weights of 0.5 gms persquare metre and 2.8 gms per square metre.

                                      TABLE 3                                     __________________________________________________________________________    EXAMPLE                                                                              COMPONENT                                                                             EXTERNAL COATING (C)                                                                         INTERNAL COATING (D)                                                                         METAL (M)                        __________________________________________________________________________    25     Can end As Ex 4 - A    As Ex 4 - B    ECCS, 0.21 mm, 450                                                            N/mm.sup.2, Type 1               26     Can end As Ex 9 - A    As Ex 9 - B            "                        27     Can end As Ex 4 - B.sup.a                                                                            As Ex 4 - A            "                        28     Can end As Ex 4 - A    As Ex 22 - B.sup.b                                                                                   "                        29     Can end As Ex 9 - B.sup.b                                                                            As Ex 9 - A            "                        30     Can end As Ex 19 - A   As Ex 19 - B   ECCS, 0.21 mm, 450                                                            N/mm.sup.2, Type 2               31     Can end As Ex 16 - A   As Ex 9 - B.sup.b                                                                            ECCS, 0.21 mm, 450                                                            N/mm.sup.2, Type 1               32     Drawn Can                                                                             As Ex 9 - B.sup.b                                                                            As Ex 23 - A   ECCS, 0.18 mm, 550                                                            N/mm.sup.2, Type 1               33     Drawn Can                                                                             As Ex 16 - A   As Ex 9 - B.sup.b                                                                                    "                        34     Drawn Can                                                                             As Ex 23 - A   As Ex 23 - B           "                        35     Can End As Ex 4 - A    As Ex 22 - B   ECCS, 0.24 mm, 550                                                            N/mm.sup.2                       36     Can End As Ex 9 - B.sup.b                                                                            As Ex 16 - A (25 micron)                                                                             "                        37     Can end As Ex 22 - A   As Ex 22 - B   Aluminium, 5182, 0.33 mm         38     Can end As Ex 9 - A    As Ex 9 - B            "                        39     DWI Can As Ex 9 - B.sup.b                                                                            As Ex 9 - A    Aluminium, 3004, 0.317 mm        40     DWI Can As Ex 16 - A   As Ex 22 - B                                    41     Aerosol Cup                                                                           As Ex 4 - A    AS Ex 15 - B   ECCS, 0.27 mm, 330                                                            N/mm.sup.2                       42     Aerosol Cup                                                                           As Ex 4 - A    As Ex 4 - B (200 micron)                                                                             "                        43     Aerosol Cup                                                                           As Ex 8 - A    As Ex 8 - B (160 micron)                                                                             "                        44     Aerosol Cone                                                                          As Ex 4 - A    As Ex 22 - B   ECCS, 0.33 mm, 350                                                            N/mm.sup.2                       45     Aerosol Cone                                                                          As Ex 9 - B.sup.b                                                                            As Ex 9 - A            "                        46     Aerosol Dome                                                                          As Ex 9 - B.sup.b                                                                            As Ex 9 - A    ECCS, 0.26 mm, 450                                                            N/mm.sup.2                       47     Aerosol Dome                                                                          As Ex 16 - A   As Ex 16 - B           "                        48     Aerosol Dome                                                                          As Ex 9 - A    As Ex 9 - B            "                        49     Aerosol Dome                                                                          As Ex 16 - A   As Ex 16 - B (40 micron)                                                                     ECCS, 0.26 mm, 450                                                            N/mm.sup.2                       50     Aerosol Dome                                                                          As Ex 10 - B.sup.b                                                                           As Ex 10 - A           "                        51     Drawn Can                                                                             As Ex 4 - A    As Ex 4 - B    ECCS, 0.18 mm, 550               __________________________________________________________________________                                                 N/mm.sup.2                        Notes                                                                         .sup.a Contains 5000 ppm synthetic silica in outer five micron layer          .sup.b Contains 20% toned titanium dioxide in 29 micron centre layer, 8%      titanium dioxide and 5000 ppm synthetic silica in outer 5 micron layer.  

The coating performance of the polymer films laminated to the productsof Examples 25 to 51 was ascertained by subjecting the products tovarious tests including the following:

Double Seaming

73 mm diameter can ends were formed from the laminate curled. The endswere seamed onto welded seam can bodies using a conventional end seamingmachine.

The coating was studied for fibrillation, scuffing or damage. Coatingcoverage was assessed by immersion in acidifed copper sulphate for twominutes and visual inspection for copper deposits.

Formability

Formability was assessed by the coating coverage after cans had beenformed. Coverage was assessed as described above under Double Seaming.

Protection

Protection was gauged by accelerated tests simulating packing withagressive products for 6 to 12 months, enamel rater values and actualshelf life tests with specific products.

    ______________________________________                                        Typical accelerating media                                                                     acetic acid (1.5%)                                                            sodium chloride (1.0%) in                                                     water                                                                         citric acid (0.63%)                                                           sodium chloride (1.0%)                                                        malic acid (0.42%)                                                            water to pH 4.3                                              Typical test conditions                                                                        retort at 121° C. for one                                              hour                                                                          store for 24 hours                                           Components or cans were inspected after the test and the                      extent of corrosion compared with conventionally coated                       containers.                                                                   Enamel Rater Values                                                                            Sodium chloride solution                                                      6.4 volts                                                                     Monitor current                                                               2 mA acceptable limit                                        ______________________________________                                    

End Sealing

Polymer coated ends were seamed or swaged in the case of valve cups ontotheir counter part can body or component, using no lining compounds.Cans were filled with product and pressurised. Weight loss measurementswere made to compare propellant loss rates with conventional componentshaving lining compound. A loss rate lower than conventional was regardedas acceptable.

Some of the advantageous properties of the products of Examples 25 to 51are set out below:

    ______________________________________                                        Examples     Properties                                                       ______________________________________                                        25-31        Good external double seaming                                                  protection, and good protection.                                 28, 29, 31   Attractive white appearance.                                     32-34, 51    Good formability and protection.                                 32, 33       Attractive white appearance.                                     35-38        Good external double seaming                                                  protection and protection.                                       35           Can end requires no lining                                                    compound.                                                        39, 40       Good formability and protection.                                 41-43        Cup requires no sealing compound.                                             Excellent protection.                                            44           Cone requires no lining compound.                                45           Attractive white external                                                     appearance.                                                      46, 50       Attractive white external                                                     appearance.                                                      48, 49       Dome requires no lining compound.                                ______________________________________                                    

What is claimed is:
 1. A process for producing by simultaneouslamination a polymer/metal/polymer laminate, which process compriseslaminating to one of the major surfaces of a metal sheet a compositepolyester film (A) comprising an inner layer (A1) of a substantiallynon-crystalline linear polyester having a softening point below 150° C.and a melting point above 150° C. but below 240° C. and an outer layer(A2) of a linear polyester having a melting point above 220° C., andsimultaneously laminating to the other major surface of the metal sheeta polyolefin-containing film (B) comprising a bonding resin which is anacid modified polyolefin-resin containing carboxyl or anhydride groups,the metal sheet having been heated to a temperature T₁ sufficient tocause softening of the polymer films and intimate contact with the metalsheet, the temperature T₁ being below the temperature at which the outersurface of the polyolefin-containing film is damaged during lamination,and re-heating the resultant laminate to a temperature T₂ sufficient tocause each of the polymer films (A1) and (B) to interact with and becomebound to the respective surface of the metal sheet.
 2. A processaccording to claim 1, wherein the temperature T₁ is from 120 to 240° C.3. A process according to claim 1, wherein the laminate is reheated byinduction heating means.
 4. A process according to claim 1, wherein thelaminate is reheated by infra-red heating means.
 5. A process accordingto claim 1, wherein the temperature T₂ is from 230° to 270° C.
 6. Aprocess according to claim 5, wherein the laminate is heated to atemperature in the range 230° to 270° C. and then held above 200° C. forat least 1 second before being quenched.
 7. A process according to claim6, wherein the laminate is heated to a temperature of 250° C., and thenheld above 240° C. for 2 seconds before being quenched.
 8. A processaccording to claim 6, wherein the laminate is quenched rapidly anduniformly.
 9. A process according to claim 6, wherein the laminate isquenched rapidly and uniformly by immersion in a tank of water or byline quenching with water.
 10. A process according to claim 1, whereinthe polyester of inner layer (A1) is a copolymer of ethyleneterephthalate and ethylene isophthalate, or a copolymer formed fromterephthallic acid and two alcohols.
 11. A process according to claim10, wherein the mole ratio of ethylene terephthalate to ethyleneisophthalate is 80:20.
 12. A process according to claim 1, wherein theouter layer (A2) is a biaxially oriented polyester.
 13. A processaccording to claim 12, wherein the polyester of outer layer (A2) has acrystallinity greater than 30%.
 14. A process according to claim 12,wherein the polyester of outer layer (A2) has a crystallinity from 40 to50%.
 15. A process according to claim 1, wherein the outer layer (A2) ispolyethylene terephthalate.
 16. A process according to claim 1, whereinthe polyolefin-containing film (B) is a monolayer of, or is a compositefilm comprising (a) an inner layer (B1), of a bonding resin chosen froma maleic anhydride modified propylene, maleic anhydride modifiedpolyethylene, maleic anhydride modified ethylene-propylene copolymer, ormaleic anhydride modified ethylene-vinylacetate copolymer, and (b) anouter layer (B2) of a polyolefin or polyamide adhered to inner layer(B1).
 17. A process according to claim 16, wherein the maleic anhydridecontent of the bonding resin is from 0.05 to 0.5%.
 18. A processaccording to claim 16, wherein the maleic anhydride content of thebonding resin is from 0.1 to 0.25%.
 19. A process according to claim 1,wherein the polyolefin-containing film (B) is a monolayer of, or is acomposite film comprising (a) an inner layer (B1) of, a bonding resinchosen from an ethylene-acrylic acid copolymer or anethylene-methacrylic acid copolymer, and (b) an outer layer (B2) of apolyolefin or polyamide adhered to inner layer (B1).
 20. A processaccording to claim 1, wherein the polyolefin-containing film (B) is acomposite film comprising an inner layer (B1) of bonding resin and anouter layer (B2) of a polyolefin or polyamide adhered to inner layer(B1).
 21. A process according to claim 20, wherein thepolyolefin-containing film comprises a further polyolefin or polyamidelayer (B4) adhered to layer (B2) by means of an intermediate layer (B3)of bonding resin.
 22. A process according to claim 1, wherein the metalsheet is steel coated with a layer of chromium metal, followed by alayer of chromium oxide.
 23. A process according to claims 1, whereinthe polyester of inner layer (A1) is a copolymer of ethyleneterephthalate and ethylene isophthalate, or a copolymer formed fromterephthallic acid and ethylene glycol and cryclohexanedimethanol.
 24. Aprocess according to claim 23, wherein the mole ratio of ethyleneterephthalate to ethylene isophthalate is 80:20.
 25. A process accordingto claim 1, wherein the outer layer (A2) is biaxially orientedpolyethylene terephthalate.
 26. A process according to claim 1, whereinthe polyolefin-containing film (B) is a monolayer of, or is a compositefilm comprising (a) an inner layer (B1) of, a bonding chosen from anethylene-acrylic acid copolymer or an ethylene-methacrylic acidcopolymer containing from 5 to 15% by weight of acid, and (b) an outerlayer (B2) of a polyolefin or polyamide adhered to inner layer (B1). 27.A polymer/metal/polymer laminate comprising a metal sheet having apolymer film adhered to each of its major surfaces, the polymer filmshaving been adhered to the metal sheet by simultaneous thermallamination, the polymer film adhered to one major surface of the metalsheet being a composite polyester film (A) comprising an inner layer(A1) of a substantially non-crystalline linear polyester having asoftening point below 150° C. and a melting point above 150° C. butbelow 240° C. and an outer layer (A2) of a linear polyester having amelting point above 220° C., and the polymer film adhered to the othermajor surface of the metal sheet being a polyolefin-containing film (B)comprising a bonding resin which is an acid modified polyolefin resincontaining carboxyl or anhydride groups.
 28. A laminate according toclaim 27, wherein the polyester of inner layer (A1) is a copolymer ofethylene terephthalate and ethylene isophthalate, or a copolymer formedfrom terephthallic acid and two alcohols.
 29. A laminate according toclaim 28, wherein the mole ratio of ethylene terephthalate to ethyleneisophthalate is 80:20.
 30. A laminate according to claim 27, wherein theouter layer (A2) is a biaxially oriented polyester.
 31. A laminateaccording to claim 30, wherein the polyester of outer layer (A2) has acrystallinity greater than 30%.
 32. A laminate according to claim 30,wherein the polyester of outer layer (A2) has a crystallinity from 40 to50%.
 33. A laminate according to claim 27, wherein the outer layer (A2)is polyethylene terephthalate.
 34. A laminate according to claim 27,wherein the polyolefin-containing film (B) is a monolayer of, or is acomposite film comprising (a) an inner layer (B1), of a bonding resinchosen from a maleic anhydride modified propylene, maleic anhydridemodified ethylene-propylene copolymer, maleic anhydride modifiedpolyethylene, or maleic anhydride modified ethylene-vinylacetatecopolymer, and (b) an outer layer (B2) of a polyolefin or polyamideadhered to inner layer (B1).
 35. A laminate according to claim 34,wherein the maleic anhydride content of the bonding resin is from 0.05to 0.5%.
 36. A laminate according to claim 34, wherein the maleicanhydride content of the bonding resin is from 0.1 to 0.25%.
 37. Alaminate according to claim 27, wherein the polyolefin-containing film(B) is a monolayer of, or is a composite film comprising (a) an innerlayer (B1) of, a bonding resin chosen from an ethylene-acrylic acidcopolymer or an ethylene-methacrylic acid copolymer, and (b) an outerlayer (B2) of a polyolefin or polyamide adhered to inner layer (B1). 38.A laminate according to claim 27, wherein the polyolefin-containing film(B) is a composite film comprising an inner layer (B1) of bonding resinand an outer layer (B2) of a polyolefin or polyamide adhered to innerlayer (B1).
 39. A laminate according to claim 38, wherein thepolyolefin-containing film comprises a further polyolefin or polyamidelayer (B4) adhered to layer (B2) by means of an intermediate layer (B3)of bonding resin.
 40. A laminate according to claim 27, wherein themetal sheet is steel coated with a layer of chromium metal followed by alayer of chromium oxide.
 41. A laminate according to claim 27, whereinthe polyester of inner layer (A1) is a copolymer of ethyleneterephthalate and ethylene isophthalate, or a copolymer formed fromterephthallic acid and ethylene glycol and cryclohexane-dimethanol. 42.A laminate according to claim 41, wherein the mole ratio of ethyleneterephthalate to ethylene isophthalate is 80:20.
 43. A laminateaccording to claim 41, wherein the outer layer (A2) is a biaxiallyoriented polyester.
 44. A laminate according to claim 27, wherein theouter layer (A2) is biaxially oriented polyethylene terephthalate.
 45. Alaminate according to claim 27, wherein the polyolefin-containing film(B) is a monolayer of, or is a composite film comprising (a) an innerlayer (B1) of, a bonding resin chosen from an ethylene-acrylic acidcopolymer or an ethylene-methacrylic acid copolymer containing from 5 to15% by weight of acid, and (b) an outer layer (B2) of a polyolefin orpolyamide adhered to inner layer (B1).
 46. A container or a componentfor a container produced from a polymer/metal/polymer laminatecomprising a metal sheet having a polymer film adhered to each of itsmajor surfaces, the polymer films having been adhered to the metal sheetby simultaneous thermal lamination, the polymer film adhered to onemajor surface of the metal sheet being a composite polyester film (a)comprising an inner layer (A1) of a substantially non-crystalline linearpolyester having a softening point below 150° C. and a melting pointabove 150° C. but below 240° C. and an outer layer (A2) of a linearpolyester having a melting point above 220° C., and the polymer filmadhered to the other major surface of the metal sheet being apolyolefin-containing film (B) comprising a bonding resin which is anacid modified polyolefin resin containing carboxyl or anhydride groups.